explicitly list all required packages

Instead of relying on the Symfony FrameworkBundle to pull in all our
needed dependencies, we should explicitly list all of them. This will
ensure that nothing breaks when the FrameworkBundle stops depending on
some optional dependencies (which was done recently).

Author: xabbuh

composer.json

@@ -23,9 +23,17 @@
     "require": {
         "php":                            "^5.5.9|~7.0",
         "psr/log":                        "^1.0",
-        "symfony/framework-bundle":       "^2.7|^3.0",
+        "symfony/config":                 "^2.7|^3.0",
+        "symfony/debug":                  "^2.7|^3.0",
+        "symfony/dependency-injection":   "^2.7|^3.0",
+        "symfony/event-dispatcher":       "^2.7|^3.0",
         "symfony/finder":                 "^2.7|^3.0",
+        "symfony/framework-bundle":       "^2.7|^3.0",
+        "symfony/http-foundation":        "^2.7|^3.0",
+        "symfony/http-kernel":            "^2.7|^3.0",
         "symfony/routing":                "^2.7|^3.0",
+        "symfony/security-core":          "^2.7|^3.0",
+        "symfony/templating":             "^2.7|^3.0",
         "doctrine/inflector":             "^1.0",
         "willdurand/negotiation":         "^2.0",
         "willdurand/jsonp-callback-validator": "^1.0"